Semiconductor devices such as DRAM (Dynamic Random Access Memory) are sometimes configured in such a way that the impedance of an output buffer circuit can be switched according to an operating mode. For example in semiconductor devices described in patent literature articles 1 and 2, an output buffer circuit is configured from a plurality of unit buffers having the same impedance as each other, and the impedance can be switched by selecting the number of unit buffers to activate. With the semiconductor devices described in patent literature articles 1 and 2, because each unit buffer has the same impedance, a calibration operation to adjust the impedance of the unit buffers can be executed in one batch.